Studies of the role of ischemia/reperfusion and superoxide anion radical production in the teratogenicity of cocaine

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs causing failed abortion in humans

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs with human abortive potential. Reactive Oxygen Species (ROS) can be harmful to embryonic tissues. The adverse embryonic effects are dependent on the severity and duration of the hypoxic event and when during organongenesis hypoxia occurs. The vascular endothelium of recently formed arteries in the embryo is highly susceptible to ROS damage. Endothelial damage results in vascular disruption, hemorrhage and maldevelopment of organs, which normally should have been supplied by the artery. ROS can also induce irregular heart rhythm in the embryo resulting in alterations in blood flow and pressure from when the tubular heart starts beating. Such alterations in blood flow and pressure during cardiogenesis can result in a variety of cardiovascular defects, for example transpositions and ventricular septal defects. One aim of this article is to review and compare the pattern of malformations produced by transient embryonic hypoxia of various origins in animal studies with malformations associated with transient embryonic hypoxia in human pregnancy due to a failed abortion process. The results show that transient hypoxia and compounds with potential to cause failed abortion in humans, such as misoprostol and hormone pregnancy tests (HPTs) like Primodos, have been associated with a similar spectrum of teratogenicity. The spectrum includes limb reduction-, cardiovascular- and central nervous system defects. The hypoxia-ROS related teratogenicity of misoprostol and HPTs, is likely to be secondary to uterine contractions and compression of uterinoplacental/embryonic vessels during organogenesis.

Cardiovascular Mitochondrial Dysfunction Induced by Cocaine: Biomarkers and Possible Beneficial Effects of Modulators of Oxidative Stress

Cocaine abuse has long been known to cause morbidity and mortality due to its cardiovascular toxic effects. The pathogenesis of the cardiovascular toxicity of cocaine use has been largely reviewed, and the most recent data indicate a fundamental role of oxidative stress in cocaine-induced cardiovascular toxicity, indicating that mitochondrial dysfunction is involved in the mechanisms of oxidative stress. The comprehension of the mechanisms involving mitochondrial dysfunction could help in selecting the most appropriate mitochondria injury biological marker, such as superoxide dismutase-2 activity and glutathionylated hemoglobin. The potential use of modulators of oxidative stress (mitoubiquinone, the short-chain quinone idebenone, and allopurinol) in the treatment of cocaine cardiotoxic effects is also suggested to promote further investigations on these potential mitochondria-targeted antioxidant strategies.

The spatio-temporal expression pattern of cytoplasmic Cu/Zn superoxide dismutase (SOD1) mRNA during mouse embryogenesis

The cytoplasmic Cu/Zn-superoxide dismutase (SOD1) represents along with catalase and glutathione peroxidase at the first defense line against reactive oxygen species in all aerobic organisms, but little is known about its distribution in developing embryos. In this study, the expression patterns of SOD1 mRNA in mouse embryos were investigated using real-time RT-PCR and in situ hybridization analyses. Expression of SOD1 mRNA was detected in all embryos with embryonic days (EDs) 7.5-18.5. The signal showed the weakest level at ED 12.5, but the highest level at ED 15.5. SOD1 mRNA was expressed in chorion, allantois, amnion, and neural folds at ED 7.5 and in neural folds, notochord, neuromeres, gut, and primitive streak at ED 8.5. In central nervous system, SOD1 mRNA was expressed greatly in embryos of EDs 9.5-11.5, but weakly in embryos of ED 12.5. At EDs 9.5-12.5, the expression of SOD1 mRNA was high in sensory organs such as tongue, olfactory organ (nasal prominence) and eye (optic vesicle), while it was decreased in ear (otic vesicle) after ED 10.5. In developing limbs, SOD1 mRNA was greatly expressed in forelimbs at EDs 9.5-11.5 and in hindlimbs at EDs 10.5-11.5. The signal increased in liver, heart and genital tubercle after ED 11.5. In the sections of embryos after ED 13.5, SOD1 mRNA was expressed in various tissues and especially high in mucosa and metabolically active sites such as lung, kidney, stomach, and intestines and epithelial cells of skin, whisker follicles, and ear and nasal cavities. These results suggest that SOD1 may be related to organogenesis of embryos as an antioxidant enzyme.

Embryonic cardiac arrhythmia and generation of reactive oxygen species: common teratogenic mechanism for IKr blocking drugs

In the adult organism, it is well established that hypoxia followed by reperfusion may be fatal and result in generation of reactive oxygen species (ROS) and subsequent tissue damage. There is also considerable evidence that temporary decrease or interruption in oxygen supply to the embryo and ROS generation during reperfusion result in tissue damage in embryonic tissues. A wide spectrum of different malformations by transient embryonic hypoxia could be produced, depending on the duration, extent, and timing of the hypoxic event. It is the contention of this paper that drugs that block the potassium channel IKr, either as an intended pharmacologic effect or as an unwanted side-effect, are potentially teratogenic by a common ROS related mechanism. Drugs blocking the IKr channel, such as almokalant, dofetilide, phenytoin, cisapride and astemizole, do all produce a similar pattern of hypoxia-related malformations. Mechanistic studies show that the malformations are preceded by embryonic cardiac arrhythmia and periods of hypoxia/reoxygenation in embryonic tissues. Pretreatment or simultaneous treatment with radical scavengers with capacity to capture ROS, markedly decrease the teratogenicity of different IKr blocking drugs. A second aim of this review is to demonstrate that the conventional design of teratology studies is not optimal to detect malformations caused by IKr blocking drugs. Repeated high doses result in high incidences of embryonic death due embryonic cardiac arrhythmia, thus masking their teratogenic potential. Instead, single dosing on specific days is proposed to be a better way to characterize the teratogenic potential of Ikr blocking drugs.

Alterations in the expression of antioxidant genes and the levels of transcription factor NF-Kappa B in relation to diabetic embryopathy in the cohen diabetic rat model

BACKGROUND

We have previously shown that oxidative stress is important in the pathogenesis of diabetes-induced anomalies in Cohen Diabetic sensitive (CDs) rat embryos and seems to interplay with genetic factors. We investigated the role of genetic factors related to the antioxidant defense mechanism in CDs rat embryos.

METHODS

We studied 11.5- and 12.5-day embryos of Cohen Diabetic resistant (CDr) and CDs rats that were fed a regular diet (RD), and hence not diabetic, compared to rats fed a high-sucrose low-copper diet (HSD) where only the CDs animals became diabetic. Embryos were monitored for growth and congenital anomalies. mRNA of catalase (CAT), glutathione peroxidase (GSHpx), CuZn-SOD (SOD-superoxide dismutase), and Mn-SOD and the extent of nuclear factor kappa B (NF-kappaB) activation were assessed.

RESULTS

Embryos of CDs dams fed RD were significantly smaller and had an increased rate of NTDs compared to embryos of CDr dams fed RD. When CDs dams were fed HSD, >50% of the CDs embryos were dead and 44% of the live embryos had NTDs. Live 11.5-day old embryos of CDs dams fed RD had a statistically significant increase in CAT, CuZn-SOD, and GSHpx mRNA levels compared with the levels in the CDr embryos from dams fed RD. CDs embryos from dams fed HSD showed significant overactivation of NF-kappaB compared with CDr embryos from dams fed HSD (in which activation was decreased), without any increase in the expression of SOD, CAT, and GSHpx.

CONCLUSIONS

This study demonstrates that one of the genetic differences between the CDr and CDs strains fed RD is an increased expression of genes encoding for antioxidant enzymes in the CDs but inability for upregulation in diabetes. In addition, while activation of NF-kappaB is decreased in CDr on HSD, it is increased in the CDs. These differences may play a role in the increased sensitivity of the CDs embryos to diabetic-induced teratogenicity.

Role of oxidative metabolites of cocaine in toxicity and addiction: oxidative stress and electron transfer

Cocaine is one of the principal drugs of abuse. Although impressive advances have been made, unanswered questions remain concerning mechanism of toxicity and addiction. Discussion of action mode usually centers on receptor binding and enzyme inhibition, with limited attention to events at the molecular level. This review provides extensive evidence in support of the hypothesis that oxidative metabolites play important roles comprising oxidative stress (OS), reactive oxygen species (ROS), and electron transfer (ET). The metabolites include norcocaine and norcocaine derivatives: nitroxide radical, N-hydroxy, nitrosonium, plus cocaine iminium and formaldehyde. Observed formation of ROS is rationalized by redox cycling involving several possible ET agents. Three potential ones are present in the form of oxidative metabolites, namely, nitroxide, nitrosonium, and iminium. Most attention has been devoted to the nitroxide-hydroxylamine couple which has been designated by various investigators as the principal source of ROS. The proximate ester substituent is deemed important for intramolecular stabilization of reactive intermediates. Reduction potential of nitroxide is in accord with plausibility of ET in the biological milieu. Toxicity by cocaine, with evidence for participation of OS, is demonstrated for many body components, including liver, central nervous system, cardiovascular system, reproductive system, kidney, mitochondria, urine, and immune system. Other adverse effects associated with ROS comprise teratogenesis and apoptosis. Examples of ROS generated are lipid peroxides and hydroxyl radical. Often observed were depletion of antioxidant defenses, and protection by added antioxidants, such as, thiol, salicylate, and deferoxamine. Considerable evidence supports the contention that oxidative ET metabolites of cocaine are responsible for much of the observed OS. Quite significantly, the pro-oxidant, toxic effects, including generation of superoxide and lipid peroxyl radicals, plus depletion of glutathione, elicited by nitroxide or the hydroxylamine derivative, were greater than for the parent drug. The formaldehyde metabolite also appears to play a role. Mechanistic similarity to the action of neurotoxin 3,3'-iminodipropionitrile is pointed out. A number of literature strategies for treatment of addiction are addressed. However, no effective interventions are currently available. An hypothesis for addiction is offered based on ET and ROS at low concentrations. Radicals may aid in cell signaling entailing redox processes which influence ion transport, neuromodulation, and transcription. Ideas are suggested for future work dealing with health promotion. These include use of AOs, both dietary and supplemental, trapping of the norcocaine metabolite by non-toxic complexing agents, and use of nitrones for capturing harmful radical species.

The nitric oxide synthesis inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) causes limb defects in mouse fetuses: protective effect of acute hyperoxia

In the present study the relationship between exposure to the nitric oxide synthesis inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME) and the induction of limb defects, with respect to stage specificity and dose dependency, was investigated in the mouse. ICR (CD-1) mice were dosed s.c with l-NAME at 50 or 90 mg/kg on gestation d 12, 13, 14, 15, or 16. A group of animals treated with vehicle on gestation d 14 served as control. Uterine contents were evaluated for teratogenesis on gestation d 18. A treatment-related disruption of limb development was noted. The effect was dose dependent and phase specific. l-NAME became teratogenically operational on gestation d 13 and elicited its maximum effect on gestation d 14, whereas no significant teratogenicity was observed when exposure occurred after gestation d 15. In utero exposure to l-NAME also reduced embryo viability relative to controls. When the higher dose was injected on gestation d 16, a significant number of dams delivered preterm. In a parallel study, the ability of hyperoxia to prevent limb teratogenesis was investigated. To this aim, a group of l-NAME-treated animals (90 mg/kg s.c. on gestation d 14) were exposed to 98 to 100% O(2) for 12 h. l-NAME-treated mice breathing room air served as positive controls. In response to hyperoxia, a significant decrement of l-NAME-induced limb defects was found. This study characterizes for the first time the teratogenic capacity of l-NAME in the mouse. Results obtained with hyperoxia fit the hypothesis that hypoxic tissue damage may play a contributory role in l-NAME-induced limb defects.

Reduced SOD activity and increased neural tube defects in embryos of the sensitive but not of the resistant Cohen diabetic rats cultured under diabetic conditions

BACKGROUND

The role of reactive oxygen species in the etiology of diabetes-induced anomalies was studied in a genetic model of nutritionally induced Type 2 diabetes mellitus: the Cohen diabetic sensitive (CDs) and resistant (CDr) rats. We have previously shown in this model that embryopathy may be induced by a combination of genetic and environmental factors. In our study we investigated the role of the antioxidant defense mechanism, genetic predisposition or environmental factors in embryos cultured under diabetic conditions.

METHODS

CDs, CDr and Sabra rat 11.5-day old embryos were studied after 28 hr of culture in control (low glucose), high glucose, diabetic sub-teratogenic, and diabetic teratogenic media. Embryos were monitored for growth retardation and congenital anomalies. Activity of superoxide dismutase (SOD) and catalase-like (CAT) enzymes was measured in embryonic homogenates.

RESULTS

In control medium, CDs embryos were significantly underdeveloped but exhibited no anomalies and SOD activity was not significantly different from that of CDr embryos. In high glucose medium, CDs embryos were smaller than CDr and Sabra embryos and smaller than CDs embryos cultured in control medium. Neural tube defects (NTD) were found predominantly in the CDs embryos starting from 14% in the high glucose medium and increasing to 29% in the sub-teratogenic medium. In the teratogenic medium, < 50% of the CDs and Sabra embryos were alive whereas all (100%) of the CDr embryos were alive. SOD activity significantly increased in CDs embryos when cultured in the high glucose medium but was significantly reduced in the sub-teratogenic medium. SOD activity was increased significantly in the Sabra embryos cultured in the sub-teratogenic medium but did not change in CDr embryos cultured in either one of the different culture media. CAT activity did not show any significant trend in either one of the rat strains or in any of the different culture conditions.

CONCLUSIONS

Our results suggest that genetic susceptibility plays an important role in inducing underdevelopment and NTD in cultured CDs embryos in sub-teratogenic medium and in protecting the CDr embryos under the same conditions. The combination of a sub-teratogenic environment with genetic susceptibility is sufficient to reduce the activity of SOD, hence decreasing the ability of the CDs embryos to cope with diabetic sub-teratogenic environment and prevent NTD.

Copper-deficient rat embryos are characterized by low superoxide dismutase activity and elevated superoxide anions

The teratogenicity of copper (Cu) deficiency may result from increased oxidative stress and oxidative damage. Dams were fed either control (8.0 microg Cu/g) or Cu-deficient (0.5 microg Cu/g) diets. Embryos were collected on Gestational Day 12 for in vivo studies or on Gestational Day 10 and cultured for 48 h in Cu-deficient or Cu-adequate media for in vitro studies. Superoxide dismutase (SOD), glutathione peroxidase (GPX), and glutathione reductase (GR) activities were measured in control and Cu-deficient embryos as markers of the oxidant defense system. Superoxide anions were measured as an index of exposure to reactive oxygen species (ROS). No differences were found in GPX or GR activities among treatment groups. However, SOD activity was lower and superoxide anion concentrations higher in Cu-deficient embryos cultured in Cu-deficient serum compared to control embryos cultured in control serum. Even so, Cu-deficient embryos had similar CuZnSOD protein levels as controls. In the in vitro system, Cu-deficient embryos had a higher frequency of malformations and increased staining for superoxide anions in the forebrain, heart, forelimb, and somites compared to controls. When assessed for lipid and DNA oxidative damage, conjugated diene concentrations were similar among the groups, but a tendency was observed for Cu-deficient embryos to have higher 8-hydroxy-2'-deoxyguanosine concentrations than controls. Thus, Cu deficiency resulted in embryos with malformations and reduced SOD enzyme activity. Increased ROS concentrations in the Cu-deficient embryo may cause oxidative damage and contribute to the occurrence of developmental defects.

Talipes equinovarus and maternal smoking: a population-based case-control study in Washington state

BACKGROUND

Talipes equinovarus (TEV), also called congenital idiopathic clubfoot, true clubfoot and common clubfoot, is one of the most common major birth defects. Its correction is often difficult and expensive. Its etiology is poorly understood and few analytic epidemiological studies have been devoted to exploring specific risk factors for TEV.

METHODS

Our population-based study consists of 239 documented cases of idiopathic TEV obtained from hospital and outpatient sources and 365 controls identified via random digit dialing from five Western Washington counties. Structured maternal interviews were conducted by trained interviewers and multiple logistic regression used to evaluate associations between maternal smoking and birth of a child with TEV.

RESULTS

Our study shows strong associations between maternal smoking and idiopathic TEV. Case mothers were more likely to have smoked during pregnancy (OR = 2.2; 95% CI = 1.5, 3.3). Increased TEV risk was seen with increased smoking and estimates ranged from 1.5 for the lightest smokers to 3.9 for the heaviest smokers. Gender specific differences in risk were also noted with risk estimates of 1.8 (95% CI = 1.2, 3.0) for boys whose mothers smoked during pregnancy and 2.8 (95% CI = 1.4, 5.4) for girls. Trends for increased risk with higher numbers of cigarettes were noted for both genders. For isolated TEV, the overall odds ratio (OR) for smoking was 2.4 (95% CI = 1.6, 3.6) with a range from 1.4-4.6. No confounders were noted.

CONCLUSIONS

As postulated, maternal smoking during pregnancy appears to increase the risk of having a child with idiopathic clubfoot and the number of cigarettes smoked influence that risk. Further delineation of dose-response is warranted as are continued efforts to decrease maternal smoking during pregnancy.

Further evidence for the role of free radicals in the limb teratogenicity of L-NAME

BACKGROUND

L-NAME (N(G)-nitro-(L)-arginine methyl ester), a nitric oxide synthase inhibitor, causes severe limb reduction malformations when gravid rats are treated intraperitoneally on gd-17. Hemorrhages, appearing within hours of L-NAME administration, and defects at term can be significantly reduced by co-treatment with PBN (alpha-phenyl-N-t-butylnitrone), a spin trap antioxidant. We have proposed that limb defects result from ischemia-reperfusion injury. We examine the role of xanthine oxidase and ROS formation in the limb effects of L-NAME.

METHODS

Gravidas were treated with L-NAME (50 mg/kg) in the presence or absence of allopurinol, a xanthine oxidase inhibitor. Spatial patterns of limb hemorrhage were determined promptly and at term as was digit length at the latter interval. Xanthine oxidase activities were assayed in control and treated limbs with and without allopurinol co-treatment.

RESULTS

Allopurinol significantly reduced hemorrhage severity in a dose-responsive fashion when fetuses were examined at term. Higher doses of allopurinol significantly preserved digit length. Xanthine oxidase activities in fetal limb were significantly increased by L-NAME treatment whereas co-treatment with allopurinol restored activities to near-control levels.

CONCLUSIONS

These findings support the role of excess reactive oxygen species (ROS) formation in L-NAME-induced limb reduction. We propose that nitric oxide (NO) depletion by L-NAME interferes with vascular integrity, and causes vasoconstriction. Resultant hypoxia stimulates superoxide formation and nitric oxide formation catalyzed by the inducible isoform of nitric oxide synthase. The reduction products of superoxide or the products of its reaction with nitric oxide oxidize or nitrate endothelial components resulting in limb reduction defects.

Embryonic arrhythmia by inhibition of HERG channels: a common hypoxia-related teratogenic mechanism for antiepileptic drugs?

PURPOSE

There is evidence that drug-induced embryonic arrhythmia initiates phenytoin (PHT) teratogenicity. The arrhythmia, which links to the potential of PHT to inhibit a specific potassium channel (Ikr), may result in episodes of embryonic ischemia and generation of reactive oxygen species (ROS) at reperfusion. This study sought to determine whether the proposed mechanism might be relevant for the teratogenic antiepileptic drug trimethadione (TMO).

METHODS

Effects on embryonic heart rhythm during various stages of organogenesis were examined in CD-1 mice after maternal administration (125-1,000 mg/kg) of dimethadione (DMO), the pharmacologically active metabolite of TMO. Palatal development was examined after administration of a teratogenic dose of DMO and after simultaneous treatment with DMO and a ROS-capturing agent (alpha-phenyl-N-tert-butyl-nitrone; PBN). The Ikr blocking potentials of TMO and DMO were investigated in HERG-transfected cells by using voltage patch-clamping tests.

RESULTS

DMO caused stage-specific (gestation days 9-13 only) and dose-dependent embryonic bradycardia and arrhythmia at clinically relevant maternal plasma concentrations (3-11 mM). Hemorrhage in the nasopharyngeal part of the embryonic palate (within 24 h) preceded cleft palate in fetuses at term. Simultaneous treatment with PBN significantly reduced the incidence of DMO-induced cleft palate, from 40 to 13%. Voltage patch-clamping studies showed that particularly DMO (70% inhibition), but also TMO, had Ikr blocking potential at clinically relevant concentrations.

CONCLUSIONS

TMO teratogenicity, in the same way as previously shown for PHT, was associated with Ikr-mediated episodes of embryonic cardiac arrhythmia and hypoxia/reoxygenation damage.

Involvement of mitochondria and other free radical sources in normal and abnormal fetal development

Shepard and Mackler have documented quantitative increases in mitochondrial cristae between gestational days 10 and 14 in rats accompanied by decreased glucose utilization and increased NADH oxidase activity. Findings show a shift from glycolytic to oxidative metabolism starting at around the time of implantation. Exposure to many substances that cause transient uteroplacental hypoperfusion, including cocaine, phenytoin, calcium channel blockers, and nitric oxide synthase (NOS) inhibitors, induce limb and central nervous system (CNS) malformations while sparing the heart. We have reported that isolated electron transport particles prepared from sensitive tissues show reduced NADH oxidase activities compared with insensitive heart. They also have significantly greater superoxide formation in association with significantly reduced superoxide dismutase activities. NOS inhibitors induce severe limb reductions in late gestation. Exposure is associated with hemorrhage and nitrotyrosine (NT) formation shortly after treatment. Hemorrhage, malformations, and NT formation can be significantly reduced by coadministration of PBN, allopurinol, or aminoguanidine. On the basis of these findings, we have proposed a role for the formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the genesis of limb reduction defects. It is important to note that limb reduction defects occur in humans ( approximately 0.22/1000) and have been associated with the agents listed above.

Salicylate and cocaine: interactive toxicity during chicken mid-embryogenesis

Increased free radical production, due to ischemia and reperfusion, has been postulated as a cause of cocaine's (COC) developmental toxicity. Salicylate reacts with hydroxyl free radicals (*OH) to form stable, quantifiable reaction products, which can be measured with high-pressure liquid chromatography (HPLC). To determine if chicken embryos' brains and hearts were exposed to increased *OH concentrations after injection of COC, an injection of a nontoxic dose of sodium salicylate (NaSAL, 100 mg/kg egg, or 5 mg/egg), followed by 5 injections of COC (13.5 mg/kg or 0.675 mg/egg, every 1.5 h), was administered to eggs containing embryos on the 12th day of embryogenesis (E12). In addition to finding increased *OH concentrations in E12 embryonic hearts and brains, we observed that the developmental toxicity of COC, manifest as vascular disruption (hemorrhage) and lethality, was enhanced by NaSAL injection. These results confirm and extend results of similar experiments performed upon older embryos (E18), and indicate that increased &z.rad;OH concentration in embryonic tissues after COC exposure and toxic interactions of COC and NaSAL can also occur at an earlier stage of development. The results are discussed in light of possible exposure of human fetuses to both COC and salicylates, since COC-abusing pregnant women can be misdiagnosed with pre-eclampsia and aspirin is used to treat this syndrome.

Developmental considerations of neurotoxic exposures

In this article, the authors provide a conceptual framework in which to consider alternative approaches to identify the developmental consequences of exposing the developing brain to neurotoxic substances. Concepts underlying brain development and issues regarding neurobehavioral testing in children are reviewed. In addition, the authors selectively review preclinical data identifying mechanisms contributing to neurobehavioral compromise, and clinical data identifying deficits resulting from exposure to two classes of neurotoxins: exposure to drugs of abuse, including alcohol, nicotine, and cocaine; and exposure to environmental agents, including lead, methyl-mercury, PCBs, and organophosphorus compounds.

Role of free radicals in the limb teratogenicity of L-NAME (N(G)-nitro-(L)-arginine methyl ester): a new mechanistic model of vascular disruption

In continuing studies of limb effects resulting from fetal exposure to N(G)-nitro-(L)-arginine methyl ester (L-NAME), we examined the early time course of vascular changes and the effectiveness of fetal intraamniotic injection. Vascular engorgement and hemorrhage occurred within 4 hr of L-NAME treatment on gestational day (gd) 17, and direct injection appeared to be as effective as maternal intraperitoneal injection in inducing limb hemorrhage. Further studies examined protein nitration and electron transport inhibition in tissues of exposed fetuses. L-NAME caused significant increases in nitrotyrosine (NT) formation in limb but not in heart or brain, and reduced electron transport rates in limb. Three agents, alpha-phenyl-N-t-butylnitrone (PBN), a radical trap and inhibitor of inducible nitric oxide synthase (iNOS), allopurinol, an inhibitor of xanthine oxidase, and aminoguanidine, a relatively specific inhibitor of iNOS, significantly moderated limb hemorrhage and protein nitration in distal limb. These results suggest that L-NAME works directly on the fetal limb vasculature and indicate a cytotoxic role for peroxynitrite, a potent oxidant and nitrating agent that is the reaction product of nitric oxide and superoxide anion radical. We propose that L-NAME and other vasoactive toxicants disrupt the fetal limb in a sequential process. Initially, nitric oxide (NO) is depleted, causing hemorrhage and edema in the limb. Within hours, iNOS is induced, resulting in cytotoxic tissue concentrations of NO and reactive nitrogen species that induce apoptosis and/or necrosis in the limb. We suggest that L-NAME exposure may serve as a model of vascular disruptive limb malformations.

Reactive oxygen species and DNA oxidation in fetal rat tissues

It is well recognized that reactive oxygen species (ROS) are formed during the reperfusion of ischemic tissues and ROS may be pathogenic in adult tissues. Although there is little information on the formation and toxicity of ROS during prenatal life, a strong association has been made between limb and possibly brain malformations and uteroplacental ischemia during fetal stages of gestation. It has been proposed that these malformations result from attack by ROS formed during the resumption of placental perfusion. Studies reported here examined formation of ROS in teratogenically sensitive limb and brain and insensitive heart before and during the period of teratogenic sensitivity. Also examined was the formation of ROS following hypoxia and reoxygenation in fetal culture and DNA hydroxylation in sensitive and insensitive fetal tissues during uteroplacental ischemia and reperfusion in vivo. Rates of formation of superoxide anion radical and hydrogen peroxide declined with increasing gestational age whereas those for hydroxyl radical increased. Hydrogen peroxide generation was greatest in insensitive heart whereas hydroxyl radical formation was significantly lower in brain than in limb or heart, which had comparable rates. Hydrogen peroxide generation, which declined significantly in fetuses, but not in membranes with gestation, failed to respond to reoxygenation in vitro. Finally, there were significant increases in DNA hydroxylation in fetal hearts and limbs, but not in brains during uteroplacental ischemia but no further significant change could be detected after reperfusion.

Effect of cocaine, 95% oxygen and ellagic acid on the development and antioxidant status of cultured rat embryos

Prenatal exposure to cocaine has been associated with adverse developmental effects and current data suggest cocaine induced malformations are caused by ischemic-reperfusion injury. This study was undertaken to assess a new in vitro model which uses a routine rat whole embryo culture system that incorporates a change in oxygen status, and to examine the effects of altered oxygen status and pretreatment with ellagic acid (EA), an anti-oxidant, after cocaine exposure. Embryos were evaluated by determining a developmental score and by measuring tissue reduced glutathione (GSH) levels. Following re-oxygenation with 95% O2 for the last 6 h of culture, embryos treated with cocaine had reduced developmental scores and GSH levels. Embryos treated with cocaine and not re-oxygenated with 95% O2 did not have reduced developmental scores. EA blocked the effects of cocaine on developmental score and GSH level. These data support ischemia-reperfusion injury as the mechanism of cocaine developmental toxicity.

Analysis of interdigital spaces during mouse limb development at intervals following amniotic sac puncture

A spectrum of limb abnormalities ranging from adactyly, syndactyly, acrosyndactyly to nail hypoplasia was encountered in mouse embryos subjected to amniotic sac puncture at the corresponding gestational stage when human chorionic villus sampling (cvs) would normally be performed clinically. Previous skeletal studies revealed that, apart from the occasional incidence of fusion of 2 distal phalanges, syndactyly usually only affected the soft tissues within the interdigital spaces. A similar situation was also observed in cases of adactyly; while the skeletal elements of the digits were present, the soft tissues in the interdigital spaces failed to separate. A transient period of bradycardia is induced, possibly secondary to compression of the embryo by the extraembryonic membranes and uterine muscles following amniotic sac puncture. These factors, we believe, produce temporary hypoxia/ischaemia of the distal extremities, and may lead to the modification of the interdigital mesenchymal tissues within the autopods. In order to investigate the mechanism(s) underlying soft tissue syndactyly, limbs recovered at 0.5, 4, 8, 12, 24, or 36 h following amniotic sac puncture (ASP) were examined histologically. Vascular disruption in the form of localised areas of haemorrhage, vascular dilatation and congestion and the presence of fluid-filled cavities occurred in relation to the marginal vein and vascular plexus in the interdigital spaces. It is hypothesised that this interfered with the normal equilibrium of the preset programs of mitosis/cell death and apoptosis within the mesenchymal cells of the interdigital spaces. Apoptosis in these areas was inhibited in the majority of the experimental limbs analysed 4 h after ASP. Instead of undergoing necrosis/apoptosis, increased mitotic activity was usually observed from 8 h following ASP at the sites where apoptosis would normally be expected to be seen. The aberrant fate of the interdigital mesenchyme following ASP and the underlying mechanism(s) involved are discussed, as is the critical importance of an adequate vascular supply to the interdigital spaces during the morphogenesis of the autopod. We believe that this report contributes to understanding the mechanism(s) which lead to syndactyly following ASP, and the limb defects occasionally seen following cvs when this is undertaken during early gestation.

Oxidative damage in chemical teratogenesis

The teratogenicity of many xenobiotics is thought to depend at least in part upon their bioactivation by embryonic cytochromes P450, prostaglandin H synthase (PHS) and lipoxygenases (LPOs) to electrophilic and/or free radical reactive intermediates that covalently bind to or oxidize cellular macromolecules such as DNA, protein and lipid, resulting in in utero death or teratogenesis. Using as models the tobacco carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), the anticonvulsant drug phenytoin, structurally related anticonvulsants (e.g. mephenytoin, nirvanol, trimethadione, dimethadione) and the sedative drug thalidomide, we have examined the potential teratologic relevance of free radical-initiated, reactive oxygen species (ROS)-mediated oxidative molecular target damage, genotoxicity (micronucleus formation) and DNA repair in mouse and rabbit models in vivo and in embryo culture, and in vitro using purified enzymes or cultured rat skin fibroblasts. These teratogens were bioactivated by PHS and LPOs to free radical reactive intermediary metabolites, characterized by electron spin resonance spectrometry, that initiated ROS formation, including hydroxyl radicals, which were characterized by salicylate hydroxylation. ROS-initiated oxidation of DNA (8-hydroxy-2'-deoxyguanosine formation), protein (carbonyl formation), glutathione (GSH) and lipid (peroxidation), and embryotoxicity were shown for phenytoin, its major hydroxylated metabolite 5-(p-hydroxyphenyl)-5-phenylhydantoin [HPPH], thalidomide, B[a]P and NNK in vivo and/or in embryo culture, the latter indicating a teratologically critical role for embryonic, as distinct from maternal, processes. DNA oxidation and teratogenicity of phenytoin and thalidomide were reduced by PHS inhibitors. Oxidative macromolecular lesions and teratogenicity also were reduced by the free radical trapping agent phenylbutylnitrone (PBN), and the antioxidants caffeic acid and vitamin E. In embryo culture, addition of superoxide dismutase (SOD) to the medium enhanced embryonic SOD activity, and SOD or catalase blocked the oxidative lesions and embryotoxicity initiated by phenytoin and B[a]P, suggesting a major contribution of ROS, as distinct from covalent binding, to the teratologic mechanism. In in vivo studies, other antioxidative enzymes like GSH peroxidase, GSH reductase and glucose-6-phosphate dehydrogenase (G6PD) were similarly protective. Even untreated G6PD-deficient mice had enhanced embryopathies, indicating a teratological role for endogenous oxidative stress. In cultured fibroblasts, B[a]P, NNK, phenytoin and HPPH initiated DNA oxidation and micronucleus formation, which were inhibited by SOD. Oxidation of DNA may be particularly critical, since transgenic mice with +/- or -/- deficiencies in the p53 tumor suppressor gene, which facilitates DNA repair, are more susceptible to phenytoin and B[a]P teratogenicity. Even p53-deficient mice treated only with normal saline showed enhanced embryopathies, suggesting the teratological importance of endogenous oxidative stress, as observed with G6PD deficiency. These results suggest that oxidative macromolecular damage may play a role in the teratologic mechanism of xenobiotics that are bioactivated to a reactive intermediate, as well in the mechanism of embryopathies occurring in the absence of xenobiotic exposure.

The teratogenicity of N(omega)-nitro-L-ariginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, in rats

Exposure of gravid rats to the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) in drinking water or by implanted osmotic minipumps significantly elevates maternal blood pressure, reducing uteroplacental perfusion. Administration by either route causes fetal growth retardation, but oral exposure also causes hind limb reduction malformations. The present study employed both oral and intraperitoneal routes to determine the period of sensitivity to developmental toxicity, dose-response, and possible fetotoxic mechanisms. Hind limb hemorrhage occurred only in litters from dams exposed to oral doses of 1 to 2 mg/mL from gestational days 15 through 17. In contrast to oral exposure, single intraperitoneal injections caused both fore and hind limb reductions at doses of 25 mg/kg and above administered on gestational day 16 and later. Many other exposures that reduce uteroplacental perfusion have been associated with vascular disruptive dysmorphogenesis. These exposures include phenytoin, calcium channel inhibitors, cocaine, and uterine vascular clamping. Limb hemorrhage induced by these exposures is usually limited to distal structures, typically phalanges, and the incidence of affected fetuses rarely exceeds 50%. By contrast, hemorrhage caused by L-NAME frequently involves entire limbs, extending into adjacent flank in severe instances, and 100% of fetuses from treated dams may be affected. The basis of this difference and the differing defect patterns associated with the various routes of exposure are unclear, but the generation of reactive oxygen species during resumption of normal perfusion may play a role in this vascular disruption.

Free radicals and ethanol-induced cytotoxicity in neural crest cells

Associations between ethanol-induced cranial neural crest cell (NCC) damage in mammalian embryos and subsequent malformations as observed in human fetal alcohol syndrome have previously been illustrated. The vulnerability of NCCs to this teratogen may result, at least in part, from their sensitivity to free radical damage. To examine relationships between free radical generation and NCC cytotoxicity, primary culture of mouse NCCs was used. NCC viability was determined in both dose- and time-response studies involving ethanol exposure. After 48 hr of culture, cell viability was significantly diminished at all doses tested (i.e., 50, 100, 150, and 200 mM ethanol). At 100 mM ethanol (a dosage that is teratogenic in vivo and in whole embryo culture), cell viability decreased to approximately 50% of control values over the first 12 hr of culture, and decreased further, to approximately 20% by 48 hr. Using nitroblue tetrazolium as a probe, it was observed that exposure of NCCs to ethanol stimulated the production of superoxide anion radicals. Co-treatment of the ethanol-exposed NCCs with free radical scavengers including 300 units/ml of superoxide dismutase, catalase (500 units/ml), or alpha-tocopherol (300 microM) significantly improved NCC viability. These results suggest that the ethanol-induced NCC injury is mediated, at least in part, through the generation of free radicals. To test this hypothesis further, NCCs were exposed in culture to xanthine/xanthine oxidase. Exogenous free radicals generated by the xanthine/xanthine oxidase system resulted in reduced NCC viability, the severity of which increased in a time and enzyme concentration-related manner. Superoxide dismutase (300 units/ml) and catalase (500 units/ml) significantly reduced the effects of the xanthine/xanthine oxidase-generated free radicals on NCC viability. The similarity between the susceptibility of NCCs to ethanol and their susceptibility to exogenous free radicals in concert with the free radical scavenger-mediated amelioration of ethanol and exogenous free radical-induced NCC death strongly suggest that free radicals play a significant role in ethanol-induced NCC death.

Teratogenic potential of cocaine

Cocaine has been implicated as a potential cause of congenital abnormalities since the mid 1980s. Clinical studies have reported an increased risk of cardiovascular and central nervous system abnormalities as well as an increased incidence of limb reduction defects and intestinal atresias. The published data have not established an unequivocal link between cocaine and these abnormalities. The most compelling evidence for the role of cocaine as a teratogen is the increased risk of genitourinary tract defects. Although animal models have also yielded contradictory conclusions, it is intriguing to note that the abnormalities observed in these models are similar to those seen clinically. This review summarizes the clinical and basic research relating to the teratogenic potential of cocaine.

Biochemical toxicology of chemical teratogenesis

Although exposure during pregnancy to many drugs and environmental chemicals is known to cause in utero death of the embryo of fetus, or initiate birth defects (teratogenesis) in the surviving offspring, surprisingly, little is known about the underlying biochemical and molecular mechanisms, or the determinants of teratological susceptibility, particularly in humans. In vitro and in vivo studies based primarily on rodent models suggest that many potential embryotoxic xenobiotics are actually proteratogens that must be bioactivated by enzymes such as the cytochromes P450 and peroxidases such as prostaglandin H synthase to teratogenic reactive intermediary metabolites. These reactive intermediates generally are electrophiles or free radicals that bind covalently (irreversibly) to, or directly of indirectly oxidize, embryonic cellular macromolecules such as DNA, protein, and lipid, irreversibly altering cellular function. Target oxidation, known as oxidase stress, often appears to be mediated by reactive oxygen species (ROS) such as hydroxyl radicals. The precise nature of the teratologically relevant molecular targets remains to be established, as do the relative conditions of the various types of macromolecular lesions. Teratological suseptibility appears to be determined in part by a balance among pathways of maternal xenobiotic elimination, embryonic xenobiotic bioactivation and detoxification of the xenobiotic reactive intermediate, direct and indirect pathways for the detoxification of ROS (cytoprotection), and repair of macromolecular lesions. Due largely to immature or otherwise compromised embryonic pathways for detoxification, Cytoprotection, and repair, the embryo is relatively susceptible to reactive intermediates, and teratogenesis via this mechanism can occur from exposure to therapeutic concentrations of drugs, or supposedly safe concentrations of environmental chemicals. Greater insight into the mechanisms involved in human reactive intermediate-mediated teratogenicity, and the determinants of individual teratological susceptibility, will be necessary to reduce the unwarranted embryonic attrition from xenobiotic exposure.

Studies of mitochondria in oxidative embryotoxicity

While the limb bud and brain of the rat develop abnormally in response to transient uteroplacental hypoperfusion during late gestation, the heart appears to be protected. These malformations have been associated with the generation of reactive oxygen species (ROS). Studies were designed to examine superoxide generation by mitochondrial electron transport particles (ETP) from adult and conceptal tissues and to investigate characteristics that could be responsible for heightened concentrations of ROS in sensitive tissues. Parameters investigated included NADH oxidase and cytochrome c oxidase activities, cytochrome content, and superoxide dismutase activity. NADH oxidase activities were significantly lower in sensitive tissues that also developed the highest concentrations of superoxide. Because ETP from adult CNS also had low NADH oxidase activity but did not show increased concentrations of superoxide, inhibition of electron transport did not adequately account for increased ROS concentrations. The reduced NADH oxidase activity of sensitive tissues could not be caused by inhibition at the cytochrome c oxidase region since this latter activity equaled or exceeded the former in all instances. No significant differences were found in the cytochrome contents of different tissues. There was significantly less superoxide dismutase activity in homogenates prepared from either of the two sensitive conceptual tissues compared with those from insensitive conceptual or adult tissues. These studies confirm the presence of heightened concentrations of superoxide anion radical in ETP from teratogenically sensitive tissues and suggest that these concentrations may result primarily from decreased activity of superoxide dismutase(s) in those tissues. Superoxide anion radical could therefore be available to participate in the generation of the more toxic oxidant species such as the hydroxyl radical.

Ethanol-induced teratogenesis: free radical damage as a possible mechanism

To investigate the possibility of a free radical mechanism for ethanol-induced teratogenesis, gestational day 8 mouse embryos were exposed for 6 hr in whole embryo culture to a teratogenic dosage of ethanol alone (500 mg%) or in conjunction with an antioxidant, superoxide dismutase (SOD; 300 U/ml). For subsequent analysis, some embryos were examined at the end of this 6-hr period, while others were removed to control medium and cultured for an additional time period. Ethanol exposure resulted in increased superoxide anion generation and increased lipid peroxidation (as noted 6 hr after initial ethanol exposure) and in excessive cell death (as noted 12 hr after initial exposure) in the embryos. Following a total of 36 hr in culture, a high incidence of malformation, including failure of the anterior neural tube to close in 63% of the ethanol-exposed embryos, was noted. The ethanol-induced superoxide anion generation, lipid peroxidation, excessive cell death, and dysmorphogenesis were diminished in embryos co-treated with SOD, suggesting that the teratogenicity of ethanol is mediated, at least in part, by free radical damage.

Possible fetal effects of cervical dilation and uterine curettage during the first trimester of pregnancy

We describe two malformed infants whose mothers had cervical dilation and uterine curettage. One mother had the procedure at 8 weeks and the other at 6 weeks of gestation. One infant had a facial cleft, hypertelorism, scalp defects, brain malformations, and absent fingernails and a constricting band on the fourth and fifth fingers. The other infant had an area of diminished scalp hair, vertebral anomalies, and a heart defect.

Effects of prenatal exposure to cocaine on heart rate and nonassociative learning and retention in infant rats

Nonassociative learning and retention were assessed in terms of habituation of a heart-rate (HR) orienting response (bradycardia) to a tone in 16-day-old male and female rats prenatally exposed to cocaine and in control offspring. Offspring were derived from Sprague-Dawley dams given daily subcutaneous injections of 40 mg/kg/3 cc cocaine HCI (C40) from gestational days 8-20, pair-fed control dams given saline injections (PF), and nontreated control dams (LC). Each pup was adapted to the test apparatus for 15 min prior to being given 10 presentations of a pulsing tone, each separated by a 65-sec intertrial interval, with HR measured during a 5-sec pretone period and throughout the 10-sec tone for each trial. To assess retention, subjects were given 10 additional tone trials either 1, 2, 4, or 6 hr later. C40 male offspring displayed significantly lower basal HR following the initial 15-min isolation period than either LC or PF offspring, whereas prenatal treatment had no effect on basal HR among females. Although no differences were seen in rate of habituation, prenatal cocaine exposure was observed to affect retention of the habituated orienting response. Whereas LC and PF offspring retained habituation of the orienting response for less than 4 hr, C40 offspring exhibited no forgetting after a 4-hr interval, and showed significant loss of the habituation response only after a 6-hr interval.

Role of oxygen free radicals in cocaine-induced vascular disruption in mice

To test the hypothesis that cocaine-induced embryonic vascular disruption is mediated by oxygen free radicals, the antioxidants 2-oxothiazolidine-4-carboxylate (OTC) and alpha-phenyl-N-t-butyl nitrone (PBN) were employed. When cocaine (78 mg/kg) was administered on day 8 of gestation to ICR mice and embryos evaluated on day 10 (in vivo), 62.3% of cocaine-treated embryos showed increased vasodilation compared to 4.9% for controls, and 33.1% of the cocaine-exposed embryos showed marked hemorrhage compared to 3.3% for controls. In addition, cocaine increased the incidence of neural defects, in the form of open neural tube, hypoplastic prosencephalon, and microcephaly. Administration of OTC (0.25 and 0.5 mmol/kg) or PBN (300 mg/kg) prior to cocaine significantly reduced cocaine-induced vasodilation and hemorrhage, while not preventing neural defects. When cocaine (78 mg/kg) was administered in vivo on day 8 of gestation and embryos were dissected 15 min later and subsequently cultured for 48 hr in the absence of cocaine (in vivo-in vitro), marked vascular disruption was observed: normal yolk circulation/heartbeat was decreased to 26.6%, while edema/blisters and vasodilation/hemorrhage were increased to 45.6% and 59.6%, respectively. Administration of PBN (300 mg/kg) prior to cocaine completely prevented cocaine-induced vascular disruption. When cocaine was administered in vivo and PBN (300 micrograms/ml) was incubated with cultured embryos in vitro, the antioxidant only partially prevented cocaine-induced cardiovascular defects in this model. Neural defects produced by cocaine were not significantly affected by PBN, administered either in vivo or in vitro. Cocaine (78 mg/kg) administered in vivo stimulated lipid peroxidation maximally after 3 hr in both day 8 and day 9 embryos. When cocaine was incubated in vitro during embryo culture at 33 micrograms/ml, a concentration that produces nonspecific inhibition of growth and development, embryonic lipid peroxidation on day 9 was not affected. Finally, when PBN (300 mg/kg) was administered prior to cocaine (78 mg/kg) on day 8 of gestation, stimulation of lipid peroxidation by cocaine was prevented. These results suggest that cocaine-induced vascular disruption in early development is mediated by maternal production of oxygen free radicals.

Ethyl alcohol reduces cardiac output, stroke volume, and end diastolic volume in the embryonic chick

It has been established that ethanol causes both human congenital cardiac malformations and structural intracardiac abnormalities in the embryonic chick. In view of a theory that reduced embryonic tissue hemodynamics are associated with the development of malformations, we attempted to determine whether or not a) ethanol altered cardiac blood flow and b) altered hemodynamics were a function of ethanol dose in the chick embryo. Cardiac function in Hamburger-Hamilton stage 19 chick embryos was recorded on videotape before and up to 10 hours after exposure to graded doses of ethanol. Parameters of cardiac function, including cardiac output, were determined from videotaped images by means of computer assistance. Cardiac output decreased in a linear fashion with dose for up to 3 hours after exposure to ethanol. The maximum relative percent decrease in cardiac output was directly related to the dose of ethanol administered. Furthermore, the time required after ethanol treatment for mean cardiac output to return to pretreatment and control values was also dose-dependent--lower doses of ethanol required less time for mean cardiac output to return to pretreatment and control values. Although relatively high doses of ethanol depress cardiac rate, we attribute the significant decrease in cardiac output primarily to parallel dose-dependent decreases in both stroke volume and end diastolic volume. Our data are consistent with the hypothesis that reduced embryonic cardiac blood flow during cardiogenesis is associated with the development of ethanol-induced intracardiac defects in chick embryos.

Chemical teratogenesis

This review has briefly summarized what is currently known concerning the mechanisms whereby several groups of chemicals regarded as "recognized" human teratogens elicit their respective teratogenic effects. It is evident that the extent of our understanding of mechanisms for individual chemicals varies dramatically from that of a reasonably good understanding for methotrexate and other folic acid antagonists to that of virtually no understanding for the most widely recognized human teratogen, thalidomide. Even with methotrexate, however, much remains to be learned pertaining to mechanisms--i.e., the critical links in the chain of events between dihydrofolate reductase inhibition and the manifestation of specific abnormalities. Nevertheless, we can take some comfort in being able to say that we understand the primary causative mechanism. For thalidomide, as well as several others the chemical represents both a shame and a challenge--a challenge that should be addressed with our most serious efforts.